Engineers typically design high-pressure oil field plunger pumps in two sections; the (proximal) power section and the (distal) fluid section. The power section usually comprises a crankshaft, reduction gears, bearings, connecting rods, crossheads, crosshead extension rods, etc. Commonly used fluid sections usually comprise a plunger pump housing having a suction valve in a suction bore, a discharge valve in a discharge bore, an access bore, and a plunger in a plunger bore, plus high-pressure seals, retainers, etc. FIG. 1 is a cross-sectional schematic view of a typical fluid section showing its connection to a power section by stay rods. A plurality of fluid sections similar to that illustrated in FIG. 1 may be combined, as suggested in the Triplex fluid section housing schematically illustrated in FIG. 2.
Valve terminology varies according to the industry (e.g., pipeline or oil field service) in which the valve is used. In some applications, the term “valve” means just the moving element or valve body. In the present application, however, the term “valve” includes other components in addition to the valve body (e.g., various valve guides to control the motion of the valve body, the valve seat, and/or one or more valve springs that tend to hold the valve closed, with the valve body reversibly sealed against the valve seat).
Each individual bore in a plunger pump housing is subject to fatigue due to alternating high and low pressures which occur with each stroke of the plunger cycle. Conventional plunger pump housings typically fail due to fatigue cracks in one of the areas defined by the intersecting suction, plunger, access and discharge bores as schematically illustrated in FIG. 3.
To reduce the likelihood of fatigue cracking in the high pressure plunger pump housings described above, a Y-block housing design has been proposed. The Y-block design, which is schematically illustrated in FIG. 4, reduces stress concentrations in a plunger pump housing such as that shown in FIG. 3 by increasing the angles of bore intersections above 90°. In the illustrated example of FIG. 4, the bore intersection angles are approximately 120°. A more complete cross-sectional view of a Y-block plunger pump fluid section is schematically illustrated in FIG. 5.
Although several variations of the Y-block design have been evaluated, none have become commercially successful for several reasons. One reason is that mechanics find field maintenance on Y-block fluid sections difficult. For example, replacement of plungers and/or plunger packing is significantly more complicated in Y-block designs than in the earlier designs represented by FIG. 1. In the earlier designs, provision is made to push the plunger distally through the plunger bore and out through an access bore (see, e.g., FIG. 3). This operation, which would leave the plunger packing easily accessible from the proximal end of the plunger bore, is impossible in a Y-block design.
Thus the Y-block configuration, while reducing stress in plunger pump housings relative to earlier designs, is associated with significant disadvantages. However, new high pressure plunger pump housings that provide both improved internal access and superior stress reduction are described in U.S. Pat. Nos. 6,623,259, 6,544,012 and 6,382,940, which are incorporated herein by reference. One embodiment of a right angular plunger pump such as that described in U.S. Pat. No. 6,623,259 (hereinafter the '259 patent) is schematically illustrated in FIG. 6. It includes a right-angular plunger pump housing comprising a suction valve bore (suction bore), discharge valve bore (discharge bore), plunger bore and access bore. The suction and discharge bores each have a portion with substantially circular cross-sections for accommodating, e.g., a valve seat. Note that the illustrated portions of the suction and discharge bores that accommodate a valve seat are slightly conical to facilitate substantially leak-proof and secure placement of each valve seat in the pump housing (e.g., by press-fitting a valve seat that has an interference fit with the pump housing). Less commonly, the portions of suction and discharge bores intended to accommodate a valve seat are cylindrical instead of being slightly conical. Further, each bore (i.e., suction, discharge, access and plunger bores) comprises a transition area which interfaces with other bore transition areas.
The plunger bore of the right-angular plunger pump housing of FIG. 6 comprises a plunger bore having a proximal packing area (i.e., an area relatively nearer the power section) and a distal transition area (i.e., an area relatively more distant from the power section). Between the packing and transition areas is a right circular cylindrical area for accommodating a plunger. The transition area of the plunger bore facilitates interfaces with analogous transition areas of other bores as noted above.
Each bore transition area of the right-angular pump housing of FIG. 6 has a stress-reducing feature comprising an elongated (e.g., elliptical or oblong) cross-section that is substantially perpendicular to each respective bore's longitudinal axis. Intersections of the bore transition areas are chamfered, the chamfers comprising additional stress-reducing features. Further, the long axis of each such elongated cross-section is substantially perpendicular to a plane that contains, or is parallel to, the longitudinal axes of the suction, discharge, access and plunger bores.
An elongated suction bore transition area, as described in the '259 patent, can simplify certain plunger pump housing structural features needed for installation of a suction valve. Specifically, the valve spring retainer of a suction valve installed in such a plunger pump housing does not require a retainer arm projecting from the housing. Nor do threads have to be cut in the housing to position the retainer that secures the suction valve seat. Benefits arising from the absence of a suction valve spring retainer arm include stress reduction in the plunger pump housing and simplified machining requirements. Further, the absence of threads associated with a suction valve seat retainer in the suction bore eliminates the stress-concentrating effects that would otherwise be associated with such threads.
Threads can be eliminated from the suction bore if the suction valve seat is inserted via the access bore and the suction bore transition area and press-fit into place as described in the '259 patent. Following this, the suction valve body can also be inserted via the access bore and the suction bore transition area. Finally, a valve spring is inserted via the access bore and the suction bore transition area and held in place by a similarly-inserted oblong suction valve spring retainer, an example of which is described in the '259 patent. Note that the '259 patent illustrates an oblong suction valve spring retainer having a guide hole (for a top-stem-guided valve body), as well as an oblong suction valve spring retainer without a guide hole (for a crow-foot-guided valve body). Both of these oblong suction valve spring retainer embodiments are secured in a pump housing of the '259 patent by clamping about an oblong lip, the lip being a structural feature of the housing (see FIG. 6 for a schematic illustration of oblong lip 266 in a right angular plunger pump housing).
The '259 patent also shows how discharge valves can be mounted in the fluid end of a high-pressure pump incorporating positive displacement pistons or plungers. For well service applications both suction and discharge valves typically incorporate a traditional full open seat design with each valve body having integral crow-foot guides. This design has been adapted for the high pressures and repetitive impact loading of the valve body and valve seat that are seen in well service. However, stem-guided valves with full open seats could also be considered for well service because they offer better flow characteristics than traditional crow-foot-guided valves. But in a full open seat configuration stem-guided valves may have guide stems on both sides of the valve body (i.e., “top” and “lower” guide stems) or only on one side of the valve body (e.g., as in top stem guided valves) to maintain proper alignment of the valve body with the valve seat during opening and closing. Conventional valve designs incorporating secure placement of guides for both top and lower valve guide stems have been associated with complex components and difficult maintenance.
The '295 application, of which the present application is a continuation-in-part, describes alternative methods and apparatus related to valve stem guide and spring retainer assemblies and to plunger pump housings in which they are used. Typically, such plunger pump housings incorporate one or more of the stress-relief structural features described herein, plus one or more additional structural features associated with use of alternative valve stem guide and spring retainer assemblies in the housings. Such plunger pump housings do not, however, comprise an oblong lip (see, e.g., structure 266 in FIG. 6 as noted above) for securing a suction valve spring retainer. The absence of this oblong lip simplifies machining of the plunger pump housing, and the corresponding design results in reduced stress within the pump housing.
Illustrated embodiments in the '295 application of valve stem guide and spring retainer assemblies include, for example, a combination comprising a discharge valve lower stem guide (DVLSG), plus a suction valve top stem guide and spring retainer (SVTSG-SR), plus spacers for spacing the DVLSG a predetermined distance apart from the SVTSG-SR. Alternative embodiments comprise other combinations of structural features such as, for example, spring retainers and spacers with or without associated valve guides. Note that due to the close fit of the DVLSG within the discharge bore and of the SVTSG-SR within the suction bore, insertion or removal of these structures requires maintaining precise alignment as to rotation and angle of entry with their respective bores. Such precise alignment may be difficult to maintain during field service operations.